DataBinding + Kotlin +Viewpager

1.创建viewmodel,其中BindAdapter的方法需要是静态方法，因此需要加@JvmStatic，"app:img"相当于一个自定义属性，后面xml中会用到，当app:img设置的值发生改变的时候会触发这里的setImage方法，这里的BR要使用baseAdapter包里的BR

class ViewPagerItemModel : BaseObservable() {

    @get:Bindable
    var imageUrl: String = ""
        set(value) {
            field = value
            notifyPropertyChanged(BR.imageUrl)
        }

    companion object {
        @BindingAdapter("app:img")
        @JvmStatic
        fun setImage(view: ImageView, img: String) {
            Glide.with(view.context).load(img).into(view)
        }
    }

}

2.创建ViewPager每个Item的布局文件，使用Databinding

<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <data>

        <import type="com.example.databindingdemo.viewpager.viewmodel.ViewPagerItemModel" />

        <variable
            name="itemModel"
            type="ViewPagerItemModel" />

    </data>

    <ImageView
        android:id="@+id/iv"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:scaleType="fitXY"
        app:img="@{itemModel.imageUrl}" />

</layout>

　3.创建Viewpager的适配器，使用databingding后直接在 instantiateItem 中返回binding即可，在isViewFromObject通过binding可以获取根布局

class CommonViewPager<T> : PagerAdapter {

    var context: Context? = null
    var list: List<T>? = null
    var variableId: Int? = null
    var layoutId: Int? = null
    var inflater: LayoutInflater? = null

    constructor(
        context: Context?,
        list: List<T>?,
        variableId: Int?,
        layoutId: Int?,
        inflater: LayoutInflater?
    ) : super() {
        this.context = context
        this.list = list
        this.variableId = variableId
        this.layoutId = layoutId
        this.inflater = inflater
    }

    override fun isViewFromObject(view: View, `object`: Any): Boolean {
        val binding: ViewDataBinding = `object` as ViewDataBinding
        return view == binding.root
    }

    override fun getCount(): Int {
        return list!!.size
    }

    override fun instantiateItem(container: ViewGroup, position: Int): Any {
        //返回databingding绑定的view

        var binding: ViewDataBinding =
            DataBindingUtil.inflate(inflater!!, layoutId!!, container, true)
        binding.setVariable(variableId!!, list!![position])

        //这里我们返回binding对象 这个binding对象是isViewFromObject 和destoryItem方法中的引用

        return binding

    }

    override fun destroyItem(container: ViewGroup, position: Int, `object`: Any) {
        //移除binding 对应的view
        var binding: ViewDataBinding = `object` as ViewDataBinding
        container.removeView(binding.root)
    }

}

4.测试，创建布局，Activity中传入测试数据，通过DataBinding设置adapter

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android">

    <FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <androidx.viewpager.widget.ViewPager
            android:id="@+id/viewpager"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />
        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="12345"
            />
    </FrameLayout>

</layout>

class ViewPagerActivity : AppCompatActivity() {

    private lateinit var viewpager: ViewPager

    private val guide = arrayOf(
        "https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1576663390033&di=730d0a924db46019357729ad3962ec63&imgtype=jpg&src=http%3A%2F%2Fimg3.imgtn.bdimg.com%2Fit%2Fu%3D3992817968%2C1397776076%26fm%3D214%26gp%3D0.jpg",
        "https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1576663366853&di=8cf4396b2368802337fe5a6536bbb009&imgtype=0&src=http%3A%2F%2Fimg.zcool.cn%2Fcommunity%2F0175cd58b77c62a801219c77391932.png%401280w_1l_2o_100sh.png",
        "https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1576663366853&di=62406d7412779ddfabf9690ba2647edc&imgtype=0&src=http%3A%2F%2Fhbimg.b0.upaiyun.com%2Fbc608c9430155517e6fd15f3cc950f625cdb774b16a09-dZ7fZC_fw658",
        "https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1576663551403&di=52c6783c3745a97a7aa689e29951c6d0&imgtype=jpg&src=http%3A%2F%2Fimg1.imgtn.bdimg.com%2Fit%2Fu%3D2597631641%2C1350168820%26fm%3D214%26gp%3D0.jpg"
    )

    lateinit var lists: MutableList<ViewPagerItemModel>

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        val binding = DataBindingUtil.setContentView<ActivityViewPagerBinding>(this, R.layout.activity_view_pager)

        viewpager = binding.viewpager
        lists = ArrayList()

        initData()

        val adapter = CommonViewPager<ViewPagerItemModel>(
            this,
            lists,
            BR.itemModel,
            R.layout.view_pager_item,
            layoutInflater
        )

        viewpager.adapter = adapter
    }

    private fun initData() {
        for (i in guide) {
            val v = ViewPagerItemModel()
            v.imageUrl = i
            lists.add(v)
        }
    }
}

　　使用Glide加载，因此在Manifest中注册好网络权限，即可测试

效果图如下：

代码地址：https://github.com/yanjiepeng/DataBindingDemo/tree/master/app/src/main/java/com/example/databindingdemo/viewpager